Synchrotron X-ray scattering and IR-mapping studies of wet-spun lignin-derived carbon fibre precursor

Lignin in a blend with polyacrylonitrile (PAN) was wet-spun in various processing conditions with the aim of identifying the most influential wet-spinning parameters on the properties of lignin/PAN fibres. Morphological, chemical, and structural properties of wet-spun lignin/PAN fibres were investigated by Scanning Electron Microscopy (SEM), synchrotron Infrared Microspectroscopy (IR-mapping), and synchrotron Wide-Angle X-ray Scattering (WAXS). Although the highest concentration of the coagulation bath (65%) was found favourable for fibre cross-section circularity, it led to a significant lignin loss in the wet-spun lignin/PAN fibres. This was confirmed by IR-mapping studies that showed strong CN traces but negligible aromatic ring traces within the lignin/PAN fibres wet-spun from coagulation bath concentrations of above 50%. The axial preferred orientation of the constituting structural units of wet-spun lignin/PAN fibres showed the highest sensitivity to lignin concentration of spinning dopes as compared to the other two process variables, namely feed rate and coagulation bath concentration. A reduction in the axial preferred orientation of wet-spun fibres from 0.71 to 0.27 was observed upon increasing the lignin content from 23% to 40%. This was correlated to variations in mechanical properties of the wet-spun lignin/PAN fibres.